Assessing Effects of Petroleum Oil on Intertidal Invertebrate Communities in Sydney Harbour: Preparedness Pays Off

In August 1999, a crude oil spill of some 296 000 litres from the oil tanker Laura D’Amato occurred in Gore Cove, in inner Sydney Harbour, Port Jackson (Australia), during unloading at the terminal of the Shell Co of Australia. Our laboratory has been conducting surveys over ten years of the intertidal organisms of Port Jackson, most intensively the rock platforms, with funding from the Shell Co who wished to establish a baseline against which damage caused by an oil spill could be assessed. This enabled us to implement a ‘before and after, control and impact’ (BACI) monitoring design for the assessment of environmental harm caused by the oil spill, using temporal replication at a number of sites within Port Jackson. With baseline data in hand, this study represents one of the few occasions on which it has been possible to assess accurately both impact and recovery of biological communities in response to such a contamination event. Results showed that the three main sites subjected to the spill exhibited evidence of impact in terms of lowered abundances and changes in community structure as compared with pre-spill conditions and the reference site. Two of the impacted sites subsequently showed increases of the opportunistic, limpet-like Siphonaria denticulata, and other species imbalances, including the lack of recovery at one of the sites of the gastropod Austrocochlea porcata (previously A. constricta). However, all three impacted sites showed signs of recovery over the 12-month post-spill period. Further changes in species balance, and hence community structure, can be expected to continue at these sites over the next several years as part of post-spill recovery.